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Nic edited this page Jun 4, 2021 · 13 revisions

WaterLinked DVL A50 BlueROV2 Integration & Operation

Introduction

DVL - Doppler Velocity Logger - is a Hydro-acoustic unit which uses acoustic beams to measure distance to bottom surface and the velocity which the unit is moving across the surface. It estimates velocity relative to the sea bottom by sending acoustic waves from the four angled transducers and then measure the frequency shift (doppler effect) from the received echo. By combining the measurements of all four transducers and the time between each acoustic pulse, it is able to accurately estimate the speed and direction of the movement of vehicle.

DVL A50 Specs Summary

MECHANICAL
Device diameter : 66 mm
Device height : 25 mm
Device weight (air) : 250 g
Device weight (submerged) : 185 g
Depth rating : 300 m
Materials : Stainless steel 316 (housing) + PEEK (transducer caps)
Operating temperature : -5 to 60 °C
ELECTRICAL / INTERFACE
Input voltage : 10 - 30 V
Power consumption : 0.25 A at 12V
Power-on current surge : 1.25 A at 12V
Physical interface : 8 wires (pwr/serial/Ethernet) and cable (uncut 3 meters; PUR 6.7 mm diameter) with interface module
Indicator : Status LED (Power, Lock)
Communication : UART 115200 baud serial 3,3V + Ethernet
Protocols : Water Linked WebUI demo + Water Linked API
ACOUSTIC / PERFORMANCE
Transducer frequency : 1 MHz
Transducer setup : 4-beam convex Janus array
Transducer beam angle : 22.5 degrees
Ping rate : 4-26 Hz (adaptive to altitude)
Sensor assist : Integrated AHRS/IMU (Yost Labs TSS-NANO)
Min altitude : 5 cm
Max altitude : 50 meters (Performance at altitudes > 35 meter is dependent on seabed conditions, salinity levels etc.)
Max velocity : 3.75 m/s
Velocity resolution : 0.1 mm/s
Long term accuracy : ±1.01 % (Standard version) or ±0.1 % (Performance version)

For detailed specs, technical details, engineering drawings, please refer to Hardware Integration

Software Integration with BlueROV2

Integration of the DVL-A50 into ArduPilot Companion currently exists as a branch to the ArduPilot Companion Git repository:

https://github.com/bluerobotics/companion/tree/dvl

Follow these steps to use the DVL code:

  • Go to the DVL GUI "Configuration" page. In "Network configuration" set "Static IP" with IP address 192.168.2.95 (subnet prefix 24, gateway: 192.168.2.1 dns 192.168.2.1). Click "Apply" and then power cycle the DVL.
  • As of 01-06-2021, the installed companion version on the BlueROV2 is 0.0.24-14-gd62f472. Current newest version is 0.0.26 but not installed due to this unresolved bug). See https://bluerobotics.com/learn/bluerov2-software-setup/#update-software to check for updates.
  • Make sure the CompanionPi is connected to the internet (Check this by visiting http://192.168.2.2:2770/network)
  • Navigate to http://192.168.2.2:2770/git
  • Click "origin" -> "branches" -> "dvl"
  • Click "update"
  • Wait until the update is over and the Companion reboots
  • Refresh the page and "Water Linked" should show up in the navbar

Status Check

LED Signals

  • No green light: Power is off.

  • Flashing green light (slow): DVL loocking for bottom lock.

  • Fixed green light: DVL has bottom lock. The LED is mostly on and blinks quickly to show we are alive.

DVL Communication Protocol

Main Reference of this chapter: DVL-Protocol by WaterLinked

web interface

dvl web-GUI: http://192.168.2.95/#/

dvl setting: http://192.168.2.2:2770/waterlinked

Control Variables description
Driver Enable Enables or disables the DVL Driver
DVL IP Address Inital IP where the driver will try to find the DVL. The driver always attempts to find Waterlinked-dvl.local (mDNS hostname) in the local network, if that fails, it falls back to the IP address in this field.
Orientation Orientation of the DVL: Down is the suggested use, where the DVL points to the ocean floor, Forward is an untested mode where the dvl is mounted forward to lock position to a vertical surface in front of it.
Use as Rangefinder Allows the DVL to be used as a rangefinder (shown in QGC).
Restart DVL Service Restarts the DVL service.
Set New Origin Used for dead reckoning; this makes the ROV show up in QGC at the selected location. The position displayed in QGC is calculated by the autopilot independently of the position showed in the Water Linked DVL web interface, which is calculated by the DVL itself.
Status Shows the current Driver status, useful for troubleshooting.

Serial Protocol

The serial communication format is 115200 8-N-1 (no hardware flow control).

Packets sent to and received from the DVL start with a w and end with LF or CR+LF. The packet format is:

Start byte Direction Command Options (0 to many) Checksum End byte
w c or r x ,[option] *xx \n or \r\n

Direction is command (c) for commands issued to the DVL and the DVL replies with direction set to response (r). The commands can be sent as a string or entered one char at a time from a terminal.

The protocol can support Water Linked DVLs with different feature sets. The DVL always returns a checksum. The checksum algorithm is CRC-8 and it is formatted as a hexadecimal number using 2 lower-case charaters (ex: *c3).

Commands

Commands in the table are shown without the checksum for readability.

Command Description Response Description
wcv Get protocol version wrv,[major],[minor],[patch] Protocol version. eg: wrv,2.1.0
wcw Get product detail wrw,[name],[version],[chipID],[IP address] Where type is dvl, name is product name, version is software version, chip ID is the chip ID and optionally the IP address if connected to DHCP server: eg: wrw,dvl-a50,1.4.0,0xfedcba98765432 or wrw,dvl-a50,1.4.0,0xfedcba98765432,10.11.12.140
wrx,[details below] Velocities measured. See details below
wr? Malformed request: Response when packet cannot be understood
wr! Malformed request: Packet does not match the given checksum

Ethernet protocol (TCP)

The DVL supports sending velocity updates using the Transmission Control Protocol (TCP). The DVL runs a TCP server on port 16171. Each packet sent contains a velocity report from the DVL on JSON format.

Velocity Report

Velocity report is outputted after each measurement has been completed. The expected update rate varies depending on the altitude and will be in the range is from 2-26 Hz. The X, Y, Z axis are oriented according to the marking on the DVL. The messages are delimited by newline. The velocities measured response is on the following format: wrx,[time],[vx],[vy],[vz],[fom],[altitude],[valid],[status] wrx,[time],[vx],[vy],[vz],[fom],[altitude],[valid],[status]

Variables Unit description
time ms Milliseconds since last velocity report
vx m/s Measured velocity in x direction (m/s)
vy m/s Measured velocity in y direction
vz m/s Measured velocity in z direction
fom m/s Figure of merit, a measure of the accuracy of the measured velocities (m/s)
altitude m measurement of the distance between the transducer and the bottom (m)
valid boolean bottomlock and valid altitude and velocities (y/n)
status 0 for normal operation, 1 for high temperature warning

Velocity report is outputted after each measurement has been completed. The expected update rate varies depending on the altitude and will be in the range is from 2-26 Hz. The X, Y, Z axis are oriented according to the marking on the DVL.

Example where velocities are valid:

wrx,112.83,0.007,0.017,0.006,0.000,0.93,y,0*d2
wrx,140.43,0.008,0.021,0.012,0.000,0.92,y,0*b7
wrx,118.47,0.009,0.020,0.013,0.000,0.92,y,0*54

Example where velocity and altitude is not valid and high temperature warning is given:

wrx,1075.51,0.000,0.000,0.000,2.707,-1.00,n,1*04
wrx,1249.29,0.000,0.000,0.000,2.707,-1.00,n,1*6a
wrx,1164.94,0.000,0.000,0.000,2.707,-1.00,n,1*39

Transducer report

Transducer report is outputted after each measurement has been completed. The expected update rate varies depending on the altitude and will be in the range is from 2-26 Hz.

The distances measured form each transducer is on the following format: wrt,[dist_1],[dist_2],[dist_3],[dist_4]

Variable Description
dist_1 Measured distance to bottom from trancduser 1 (m)
dist_2 Measured distance to bottom from trancduser 2 (m)
dist_3 Measured distance to bottom from trancduser 3 (m)
dist_4 Measured distance to bottom from trancduser 4 (m)

Example where velocities are valid:

wrt,15.00,15.20,14.90,14.20*b1
wrt,14.90,15.10,14.80,14.10*ac

Example where distance is not valid on transducer 4:

wrt,14.90,15.10,14.80,-1.00*53
wrt,15.00,15.20,14.90,-1.00*71

Example of TCP report. (valid)

{"time":126.04666137695312,"vx":0.009757072664797306,"vy":0.002016076585277915,"vz":-0.0002864645794034004,"fom":0.00016600292292423546,"altitude":1.8710078001022339,
"transducers":[{"id":0,"velocity":-0.002349231392145157,"distance":2.041400194168091,"rssi":30.97574806213379,"nsd":19.906816482543945,"beam_valid":true},
{"id":1,"velocity":-0.0034521492198109627,"distance":1.9942001104354858,"rssi":38.42657470703125,"nsd":30.263219833374023,"beam_valid":true},
{"id":2,"velocity":0.00183798186480999,"distance":2.0886001586914062,"rssi":31.835567474365234,"nsd":22.06237030029297,"beam_valid":true},
{"id":3,"velocity":0.0029014351312071085,"distance":2.041400194168091,"rssi":37.41792678833008,"nsd":23.786922454833984,"beam_valid":true}],"velocity_valid":true,"status":0,"format":"json_v1"}

Example of TCP report. (invalid)

{"time":429.1646423339844,"vx":0,"vy":0,"vz":0,"fom":2.661566972732544,"altitude":-1,
"transducers":[{"id":0,"velocity":0,"distance":-1,"rssi":-37.079925537109375,"nsd":25.96938133239746,"beam_valid":false},
{"id":1,"velocity":0,"distance":-1,"rssi":-46.16178894042969,"nsd":19.031171798706055,"beam_valid":false},
{"id":2,"velocity":0,"distance":-1,"rssi":-38.94984436035156,"nsd":25.094785690307617,"beam_valid":false},
{"id":3,"velocity":0,"distance":-1,"rssi":-37.11658477783203,"nsd":26.229419708251953,"beam_valid":false}],"velocity_valid":false,"status":0,"format":"json_v1"}

Example of TCP report. (indented for readability)

{
  "time": 170.52674865722656,
  "vx": -0.00563613697886467,
  "vy": -0.007631152402609587,
  "vz": -0.007641898933798075,
  "fom": 0.001959984190762043,
  "altitude": 0.6173566579818726,
  "transducers": [
    {
      "id": 0,
      "velocity": -0.007625679485499859,
      "distance": 0.6769760251045227,
      "rssi": 38.66838836669922,
      "nsd": 18.295578002929688,
      "beam_valid": true
    },
    {
      "id": 1,
      "velocity": -0.0034413286484777927,
      "distance": 0.6769760251045227,
      "rssi": 35.403541564941406,
      "nsd": 19.518909454345703,
      "beam_valid": true
    },
    {
      "id": 2,
      "velocity": -0.006717036943882704,
      "distance": 0.6653040051460266,
      "rssi": 41.03888702392578,
      "nsd": 20.25017738342285,
      "beam_valid": true
    },
    {
      "id": 3,
      "velocity": -0.01045388076454401,
      "distance": 0.6536320447921753,
      "rssi": 31.09071922302246,
      "nsd": 17.366933822631836,
      "beam_valid": true
    }
  ],
  "velocity_valid": true,
  "status": 0,
  "format": "json_v1"
}

ROS Message

WaterLinked provides a package that turns the json output to ROS message.

Usage

Find the DVLs IP address (192.168.2.95). Once that's done, the package and it's components can be run by following these steps:

To run the publisher that listens to the TCP port and sends the data to ROS

  rosrun waterlinked_a50_ros_driver publisher.py _ip:=192.168.2.95

where _IP is replaced by the IP of the DVL, in our case 192.168.2.95. You can also display the raw DVL data in the terminal by specifying the argument "do_log_data":

To run the publisher that listens to the TCP port, displays the raw data in the DVL and sends the data to ROS

  rosrun waterlinked_a50_ros_driver publisher.py _ip:=192.168.2.95 _do_log_data:=true

To run a subscriber node that listens to the DVL topic. Helpful for debugging or checking if everything is running as it should be. Choose between "subscriber_gui.py" and "subscriber.py". The non-GUI version is used here due to limitations of companion pi with commandline interface.

  rosrun waterlinked_a50_ros_driver subscriber.py

Alternatively, publish DVL message as ROS message:

  $ roscore
  # for server node:
  $ rosrun comm_tcp server_node 16171
  # for client node:
  $ rosrun comm_tcp client_node 192.168.2.95 16171

The published ROS message looks like this:

std_msgs/Header header
  uint32 seq
  time stamp
  string frame_id
float64 time
geometry_msgs/Vector3 velocity
  float64 x
  float64 y
  float64 z
float64 fom
float64 altitude
waterlinked_a50_ros_driver/DVLBeam[] beams
  int64 id    #Transducer ID
  float64 velocity    #Velocity reported by transducer
  float64 distance    #Distance value
  float64 rssi    #RSSI
  float64 nsd    #NSD
  bool valid    #Report if beam is locked on and providing reliable data
  bool velocity_valid
int64 status
string form

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